A group of NIH-funded investigators plans to acquire a Bruker E680 electron paramagnetic resonance (EPR) spectrometer, to enhance their research on a wide range of biomedical problems. This instrument will offer two features that are not available in a commercial spectrometer in the entire upper Midwest: (1) a high-field superconducting magnet and the associated high-frequency (94 GHz, "W-band") operation, and (2) pulsed excitation and the associated time-domain detection. With this instrument, commercial EPR instrumentation has undergone a revolution similar to that of NMR in the 80s and 90s, with the advent of higher frequencies and time-domain technology providing dramatic improvements in sensitivity and resolution, providing deeper and more direct physical insight into molecular structure, dynamics, and interactions. This has produced an explosion of research opportunities, opening up whole new areas of investigation in site-directed spin- labeling (SDSL) and analysis of paramagnetic metal complexes. These instruments, manufactured only by Bruker in Germany, have already been installed in labs throughout Europe, but very few have been installed in the United States, and there is no such instrument in Minnesota, Wisconsin, or Iowa. Thus the requested instrument is needed if researchers in this region are to continue their high level of productivity in EPR applications, such as the following: Myosin Structural Dynamics (Thomas, Rayment, Titus, and Nesmelov), Regulation of Cardiac Calcium Transport (Thomas and Veglia), Biophysics of Muscle Aging (Thompson and Thomas), Metalloprotein Structure and Mechanism (Lipscomb and Que), SNARE-mediated Membrane Fusion (Shin), Structural Dynamics of Viral DNA Packaging (Anderson), and Bioenergetics of Heart Failure (Bache and Nesmelov). [unreadable] [unreadable]